Hitherto, with respect to macrocyclic lactone, many studies have been done, and about 100 compounds having a musk odor have been reported. However, at the present time, only ten or so compounds have been practically utilizable as perfume components, and cyclopentadecanolide is particularly important as a vegetable-source musk substance. Accordingly, it has been desired in the field of perfumery to provide an excellent process for producing inexpensive cyclopentadecanolide, and a large amount of literature about cyclization for producing this compound or about synthesis of starting materials for cyclization has been published.
Among a number of processes for synthesizing cyclopentadecanolide, one process industrially practiced is a process which comprises polycondensating .omega.-oxypentadecanoic acid or an ester thereof and depolymerizing it to obtain the cyclopentadecanolide of macrocyclic lactone (J. Amer. Chem. Soc., Vol. 58, 654 (1936)). In this process, there is a problem as to how .omega.-oxypentadecanoic acid, the starting material, can be economically produced.
Hitherto, the .omega.-oxypentadecanoic acid has been produced by a process comprising many synthetic steps, using natural oils such as rapeseed oil, castor oil, etc. According to this process, however, the yield is poor and the cost is high (Chem. and Ind., (1960), pp. 1334-5).
On the other hand, a process which comprises carrying out teromerization of ethylene to produce .omega.-oxypentadecanoic acid has been proposed (A. N. Nesmeyanov et al., Zh. Obshch Khim., Vol. 5, 371 (1960)). However, this process produces various kinds of by-products, thus deteriorating the yield.
Furthermore, a process which comprises introducing a side chain into a cyclic compound such as 2-ethoxycarboxycyclopentanone or thiophene, etc., and carrying out ring-cleavage to produce .omega.-oxypentadecanoic acid has been reported (U.S. Pat. No. 2,989,566, Chem. Abstracts, Vol. 55, 27059f, Sato, Preprint of Chem. Soc. Japan, No. 22 (III), p. 1509 (1969)). However, .omega.-oxypentadecanoic acid obtained by this process is expensive, not only because the above-described low molecular weight cyclic compounds are not suitable as the starting material (because of their expense), but also because expensive C.sub.10 or C.sub.11 dibasic acid is necessary in order to introduce the side chain.
Furthermore, a process which comprises carrying out light exposure and catalytic reduction of .beta.-(2-oxocyclododecyl)propionic acid or an ester thereof, as the starting material, derived from cyclododecanone obtained from butadiene, to produce .omega.-oxypentadecanoic acid or ester thereof has been disclosed in Japanese Patent Publication No. 16930/70. However, in the last decade, a marked rise in the electronic energy cost of the light exposure has suppressed the industrial merit of this process prevailing difficulties in using expensive cyclododecanone under the protection of its carbonyl group by morpholine.
Moreover, a process which comprises carrying out an addition reaction of inexpensive tetrahydrofuran with undecylenoic acid or an ester thereof, obtained by thermal decomposition of castor oil in the presence of peroxide to produce 2-tetrahydrofuran-undecanoic acid or an ester thereof, has been described in Japanese Patent Publication No. 4262/68, wherein a process for deriving .omega.-oxypentadecanoic acid or ester thereof from 2-tetrahydrofuran-undecanoic acid or ester thereof has been described in the specification. However, the process for deriving .omega.-oxypentadecanoic acid or an ester thereof from 2-tetrahydrofuran-undecanoic acid or an ester thereof is a known process (refer to G. A. Olah, Friedel-Crafts and Related Reaction, Vol. IV, p. 17). Namely, this process comprises reacting 2-tetrahydrofuran-undecanoic acid or an ester thereof with acetic acid anhydride in the presence of metal halide, such as zinc chloride, etc., converting the resulting .omega.-acetyloxypentadecenoic acid into .omega.-acetylpentadecanoic acid by a hydrogenation reaction, and thereafter saponifying it to produce .omega.-oxypentadecanoic acid. Further, in this Japanese Patent Publication No. 4262/68, a ring-cleavage reaction of the tetrahydrofuran ring by hydrogen bromide has been described. Both of these ring-cleavage processes require three steps in order to derive .omega.-oxypentadecanoic acid from 2-tetrahydrofuran-undecanoic acid or an ester thereof. In addition, materials composing the apparatus are restricted due to the use of a high temperature of 200.degree. C. under high pressure using zinc chloride, acetic acid anhydride, and hydrogen bromide, such that expensive materials such as titanium, Monel metal, etc., are required for the apparatus.
In addition to the above-described processes, there is a process which comprises carrying out cleavage of aliphatic straight-chain-or cyclic ether bond using hydrogen iodide or magnesium bromide at ordinary temperature under atmospheric pressure (C. A. Smith et al., J. Org. Chem., Vol. 41, 367 (1976) and D. J. Goldsmith et al., J. Org. Chem., Vol. 40, 3571 (1975)). However, in this process, three or more steps are required for deriving .omega.-oxypentadecanoic acid, likewise the process described in Japanese Patent Publication No. 4262/68, and, in addition, expensive hydrogen iodide and magnesium bromide are required in at least a stoichiometric amount.
On the other hand, as a process for catalytic ring-cleavage of the tetrahydrofuran ring, it has been known that the ring cleavage reaction takes place at 400.degree. C. in the presence of a Pd-C catalyst. In this case, however, products having a hydroxyl group on .omega.-position are not produced (Izv. Akad. Nauk., SSSR, Ser, Khim., 1965 (1), p. 165, Chem. Abstracts, Vol. 62, 11679 (1965)). Further, there is a report that products having a hydroxyl group on the .omega.-position are obtained (yield 40 mol%) by ring-cleavage of 2-propyltetrahydrofuran in the presence of an Ni-Al alloy catalyst at 275.degree. C. under 1 atmospheric hydrogen pressure, but products having a hyroxyl group at the .omega.-position are not obtained in the presence of the same catalyst at 250.degree. C. under 50 atmospheric hydrogen pressure (N. I. Shuikin et al., Acta. Chim. Hung. Tomus, Vol. 38, p. 115 (1963)).
As described above, the manner of cleavage changes according to the kind of catalyst and the condition of hydrogenolysis, and the yield and selectivity are not completely satisfactory. Thus, an industrially useful catalytic hydrogenolysis reaction has not yet been found.